An interdisciplinary approach towards the identification of conformationally constrained peptides as immunogens that will elicit protective immunity against AIDS is proposed. This approach will be based on the known broad HIV-1 neutralizing activity of the monoclonal antibody 2F5, which recognizes the highly conserved amino-acid sequence ELDKWA, corresponding to residues 662-667 of the HXB2 viral envelope glycoprotein, gp41. The hypothesis to be tested is that conformationally constrained peptides, designed to mimic the native or 2F5-bound conformations of the ELDKWA epitope, will elicit high tiers of neutralizing antibodies when they are conjugated to a suitable carrier protein or multivalent synthetic presentation system. A series of cystine-bridge peptides designed to favor beta-sheets, beta-turns or beta-budges will be explored, since these conformations may approximate the 2F5-bound ELDKWA conformation. This peptide series will be used to optimize the loop size and position of the 2F5 epitope. In another series of peptides, linear gp-41 fragments that incorporate alpha-methyl substitutions to produce local backbone constraints will be studied, in order to locate potential helical or beta-turn structures. A third series of analogues will test helix-locked peptides that mimic the likely native conformation of the ELDKWA- flanking regions in gp41. A second design cycle will then combine the most potent constraining features. New structural insights obtained from separate, parallel studies of combinatorial libraries of human rhinovirus/ELDKWA chimeras will also be incorporated. All synthetic peptides will be assayed for affinity to 2F5 and for HIV immunoglobulin (HIVIG). Selected peptides will then be assayed for their immunogenic potency in guinea pigs, assessed as the anti- peptide guinea-pig serum titer, and the neutralizing potency of these guinea pig antisera tested against T-cell-line-adapted (TCLA) and primary HIV-1 isolates. The solution conformations of several of the most potent peptides will also be characterized in detail by circular dichroism and proton-NMR spectroscopy. These studies should shed light on the structural requirements for 2F5-like neutralizing immune responses. Carrier-conjugated, highly constrained ELDKWA peptides may elicit, by themselves, a potent neutralizing immune response. The investigator's structure-activity data should also guide the development of new 2F5-like, HIV-1- neutralizing MAbs, and potent human rhinovirus/HIV-1 chimeras of potential use as live vaccines.